Apparatus for detecting unlevelness of a pendulously supported flux valve by subjecting the valve to a vertical magnetic field

ABSTRACT

A pendulously mounted flux valve is tested for levelness by applying a vertically oriented alternating magnetic field across the flux valve. The pickup windings on the flux valve are connected to corresponding primary windings in a transolver. The rotor of the transolver is locked in alignment with the flux valve so as to produce quadrature voltages having relative magnitudes representative of any flux valve output voltages with respect to one axis of the valve. The voltages from the transolver are passed through individual signal processors each containing a filter that passes only those signals arising from the applied alternating magnetic field and a phase sensitive demodulator. The demodulator outputs are applied to the deflection plates of a cathode ray tube so as to produce a Lissajou figure consisting of a radial line having a magnitude indicative of the amount by which the plane of the flux valve is inclined with respect to the horizontal and an orientation indicative of the direction of the inclination.

United States Patent 1 Jackson 1 Dec. 11, 1973 [75] Inventor:

[73] Assignee: Sperry Rand Corporation, New

York, N.Y.

221 Filed: Dec. 20, 1971 21 Appl. No.: 209,848

John R. Jackson, Phoenix, Ariz.

[52] US. Cl. 324/43 R, 33/361, 73/1 E [51] Int. Cl G01r 33/02 [58] Fieldof Search 324/43 R, 47;

[56] References Cited UNITED STATES PATENTS 2,887,873 5/1959 l-lalpernet al. 73/1 Primary ExaminerRobert J. Corcoran Att0rneyl-loward P. TerryTRANSOLVER L l OSCILLATOR MAGNETlZlNG COIL [57] ABSTRACT A pendulouslymounted flux valve is tested for levelness by applying a verticallyoriented alternating magnetic field across the flux valve. The pickupwindings on the flux valve are connected to corresponding primarywindings in a transolver. The rotor of the transolver is locked inalignment with the flux valve so as to produce quadrature voltageshaving relative magnitudes representative of any flux valve outputvoltages with respect to one axis of the valve. The voltages from thetransolver are passed through individual signal processors eachcontaining a filter that passes only those signals arising from theapplied alternating magnetic field and a phase sensitive demodulator.The demodulator outputs are applied to the deflection plates of acathode ray tube so as to produce a Lissajou figure consisting of aradial line having a magnitude indicative of the amount by which theplane of the flux valve is inclined with respect to the horizontal andan orientation indicative of the direction of the inclina- 6 Claims, 2Drawing Figures PHASE SENSlTlVE EMODULATOR FILTER PHASE NSITIVE ODULATORFILTER SE DEM APPARATUS FOR DETECTING UNLEVELNESS OF A PENDULOUSLYSUPPORTED FLUX VALVE BY SUBJECTING THE VALVE TO A VERTICAL MAGNETICFIELD BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to flux valves and more specifically to test apparatususeful in the calibration of such valves.

2. Description of the Prior Art Flux valves are well known devices andare frequently used in aircraft navigation equipment. Basically, a fluxvalve consists of a spider-like core of laminated metal of highpermeability. The magnetic core of a typical flux valve contains threenominally horizontal arms arrayed at 120 angles with respect to eachother. Changes in the direction of the earths magnetic flux in the planeof the core causes changes in the distribution of the flux in theindividual legs of the core. The resulting change in permeability of themagnetic core material is sensed by auxiliary circuits and used toindicate the direction of the earths field.

Since the horizontal component of the earths magnetic field contains thedirectional information, a conventional flux valve is suspendedpendulously to prevent the sensing element from detecting any componentof the vertical field. The single cycle nature of the heading errorsproduced by an unlevel flux valve are indistinguishable from the singlecycle errors produced by adjacent hard iron and permanently magnetizedmembers except for the fact that the magnitude of the unlevelness errorsare proportional to vertical field strength. This characteristic makesit impractical to compensate for such errors, so that the center ofgravity of the mechanical pendulum must be adjusted to align the planeof the electrical sensing element perpendicular to the gravity vector.

Prior art methods for determining such flux valve inclination orunlevelness involve techniques wherein the flux valve is rotated toknown azimuth headings on a precise turntable, and the errors at eachheading caused by vertical components of the earths field are resolvedby using a nomograph to determine the magnitude and direction of theinclination. Such methods, however, are laborious and time consuming.Use of the present invention permits more accurate results to beachieved with a considerable reduction, not only in test time, but alsowith less specializedtest equipment.

SUMMARY OF THE INVENTION The present invention provides means forachieving balance in a pendulously supported flux valve by subjectingthe valve to a known, vertically oriented alternating magnetic field,detecting the resultant signals induced in each leg of the flux valve,resolving these signals into quadrature components having a knownorientation with respect to the legs of the flux valve, and displayingthese components on a graphical display device so as to indicatedirectly the position and relative magnitude of any mechanical imbalancethat must be corrected.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustratingthe arrangement of components useful in practicing the invention; and

FIG. 2 is a diagram illustrating one form of display for use with theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The apparatus of the presentinvention performs two primary. functions: The detection of single cycleerrors in a flux valve under test which are caused by unlevelness, andthe display of such information so as to apprise the operator of therequired magnitude and direction of change necessary to adjust thecenter of gravity of the pendulous mass so as to restore the flux valveto a horizontal position.

Referring to FIG. 1, a magnetizing coil 11 is excited from an oscillator13. The coil contains a number of turns having a diameter sufficientlylarge to enclose the flux valve 15 under test. The coil is designed toproduce an alternating magnetic field in which the flux lines arevertically oriented in the region of the flux valve.

Single cycle errors caused by unlevelness are ordinarilyindistinguishable from the single cycle errors caused by permanentlymagnetized elements inside the flux valve and by large amounts ofmagnetized hard iron that may be located in close proximity to the fluxvalve so long as the vertical magnetic field strength remains constant.The alternating magnetic field applied to the flux valve in accordancewith the principles of the present invention provides a means ofseparating the unlevelness errors from the other cyclic errors in theoutput of the flux valve. The frequency of the alternating magneticfield must, however, be quite low in relation to the normal outputfrequency of the flux valve signal. In a typical flux valve, the signalfrequency is 800 Hertz, and during a one cycle period, i.e., l/800thseconds, the magnetic field seen by the flux valve should remainessentially constant. However, when the particular application requiresthe use of a visual display of the results, the frequency of thealternating magnetic field should be high enough to provide a continuousand jitter-free presentation on the cathode ray tube. A frequency of 60Hertz has been found satisfactory for this purpose.

By way of example, consider a flux valve of the type employing threeradial arms. The pickup coil on each arm is connected to a correspondingleg on the primary winding of a transolver 17 designated as legs A, Band C for convenience. The transolver is a well known device employingthe aforementioned primary winding 19 wound on a stator core and a rotorcore contain-ing a pair of secondary coils 21 and 23 wound in spacequadrature.

As is known in the art, the rotors of such transolvers may bemechanically locked in position, whereupon the voltages induced in thesecondary coils represent a pair of quadrature voltages havingmagnitudes representative of the sine and cosine, respectively, of thevoltages applied to the primary windings of the transolver.

In accordance with the principles of the invention, the quadraturevoltages from the transolver are applied to a pair of signal processors25 and 27. The signal processors each contain a bandpass filter adjustedto pass only the signals corresponding in frequency to the signalsinduced in the pickup windings of the flux valve under test by themagnetic field arising from the magnetizing coil 11.

The bandpass filters, which may conveniently take the form of bandpassamplifiers, are used primarily as rejection filters to exclude theeffects of steady state magnetic fields and extraneous fields varying atfrequencies other than the oscillator frequency. This removes from theflux valve output such extraneous signals as those caused by the earthsambient field and similar signals caused by nearby magnetic materialsuch as material on the person of the operator.

Each signal processor also contains a conventional phase sensitivedemodulator which accepts signals from the corresponding filter.

Phase sensitive demodulators are well known devices that compare inputsignals with a reference signal and provide an output having a magnitudeindicative of the magnitude of the input signal and a polarity dependenton whether the input signal is in phase or out of phase with thereference signal.

ln the present invention, the rotor of the transolver is locked so thatthe secondary winding is oriented in a known position with respect tothe individual legs of the flux valve. A signal from the oscillator 13is used as a reference voltage. Quadrature components from thetransolver are filtered in the corresponding signal processors andcompared with the phase of the oscillator output signal. if the plane ofthe flux valve is horizontal and therefore normal to the magnetic fluxproduced by the magnetizing coil, the system is in balance and noquadrature components are produced. Under these conditions, there is nooutput signal from either of the signal processors. If, however, theplane of the flux valve is not horizontal, the alternating magneticfield from the magnetizing coil 11 will induce net voltages in thepickup windings on the flux valve. These induced voltages will be at thefrequency of the oscillator and will have comparative magnitudes whichare a function of the degree and direction of inclination of the fluxvalve.

When the resulting signals from an unlevel flux valve are applied to thesignal processors, an output signal will be derived from each signalprocessor resembling a full wave rectified voltage having a magnitudeindicative of the degree of inclination along the corresponding axis anda polarity indicative of the sense of such inclination along the sameaxis.

The voltages from the signal processors are applied to the vertical andhorizontal deflection plates, respectively, of a cathode ray tube 29.

If the flux valve under test is not level, corresponding deflectionvoltages will be applied to the deflection plates of the cathode raytube and a Lissajou figure 31 will be produced. The Lissajou figure willappear as a radial line having a length and direction representative ofthe vector sum of the two voltages produced by the transolver.

Conveniently, the cathode ray tube and the rotor of the transolver maybe positioned so that a vertical Lissajou figure originating at thecenter of the cathode ray tube and directed upwardly may represent aninclination along a specified axis such as leg A of the flux valve. Thusthe angular displacement from a vertically upward direction willindicate the point on the perimeter of the flux valve at which anadjustment must be made in order to re-align the flux valve. The lengthof the Lissajou figure then indicates the mass which must be removed oradded to balance the flux valve so as to achieve equipoise.

The apparatus of the present invention provides an instantaneousindication of the presence of an unlevelness error as well as acontinuous indication of any changes made during the calibrationprocess. The dis play allows the operator to determine rapidly andaccurately the magnitude and angular position of the error, andinstantaneously to determine the position on the flux valve where anadjustment must be made to relocate the center of gravity of thependulous mass.

H6. 2 indicates the manner in which a display device, such as thecathode ray tube 29, may be supplied with indices to facilitate testing.Assuming that flux valves to be tested contain three radial legs, theouter portion of the tube face may be supplied with indicescorresponding to the A, B and C legs, respectively. Thus, angularmeasurements may be taken directly from the tube face.

Similarly, a circular index or tolerance ring" 33 may be applied to thetube face. The radius of the circular index may then be chosen such thata radial Lissajou figure 35 within the circular index will indicate thatthe flux valve under test is within tolerance, whereas a Lissajou figure37 extending beyond the circular index will indicate that the flux valveunder test requires a mass adjustment. The peripheral indices may thenconveniently be used to locate any required mass adjustment with respectto an identified leg of the flux valve.

Although the output voltages from the phase sensitive demodulators shownin FIG. 1 have been indicated as unfiltered pulse trains, it will beappreciated that these voltages may be filtered if desired to producesteady voltages having magnitudes indicative of the unlevelness in theflux valve.

The waveshapes indicated in FIG. 1 create the display consisting of aradial line as indicated in the figures. If the output signals from thedemodulators are filtered to give a smooth d.c. signal, the display willbe a single dot which occupies a position on the screen in accordancewith the unlevel-ness. With such a single dot display, the angle ofrotation must be computed from an imaginary center point and themagnitude of the error must be computed by measuring the distancebetween the dot and the imaginary center point of the display.

While the invention has been described in its preferred embodiment, itis to be understood that the words which have been used are words ofdescription rather than limitation and that changes within the purviewof the appended claims may be made without departing from the true scopeand spirit of the invention in its broader aspects.

I claim:

1. Apparatus for detecting unlevelness in a pendulously supported fluxvalve comprising a source of alternating current signals, means to applya vertically oriented alternating magnetic field across said flux valvein response to said alternating current signals, means to receivevoltages induced in each leg of the flux valve by said alternatingmagnetic field, means to resolve said induced voltages into quadraturecomponents having a predetermined orientation with respect to said fluxvalve, means to provide output signals indicative of the magnitude andphase of each quadrature component with respect to said alternatingcurrent signals, and means for graphically displaying said outputsignals.

2. The apparatus of claim 1 wherein the means to apply the magneticfield is a cylindrical coil adjusted to encircle a flux valve to betested and positioned with its axis vertical.

3. The apparatus of claim 2 wherein the flux valve to be tested is ofthe type containing a plurality of radially disposed nominallyhorizontal arms each containing a pickup coil, and the means to resolvesaid induced voltages is a transolver having individual primary windingscorresponding to each pickup coil in the flux valve to be tested, saidprimary windings being spatially arranged to correspond to the pickupwindings on said flux valve, said transolver further containing a pairof secondary windings arranged in space quadrature and positioned sothat the axis of one secondary winding is aligned with the axis of adesignated primary winding.

4. The apparatus of claim 3 wherein the means to provide output signalsincludes individual signal processors for each of said quadraturecomponents, each of said signal processors containing a phase sensitivedemodulator connected to receive reference signals from said source ofalternating current whereby each phase sensitive demodulator produces anoutput signal having a polarity representative of the phase relationshipof the corresponding quadrature component with respect to thealternating current from said source and a magnitude indicative of themagnitude of the corresponding quadrature component.

5. The apparatus of claim 4 wherein the graphical display means is acathode ray tube having vertical and horizontal deflection platesconnected to receive the output signals from the first and second phasesensitive demodulators, respectively.

6. The apparatus of claim 5 wherein each signal processor contains aninput filter constructed to accept only quadrature components having afrequency substantially equal to that of said alternating currentsignals.

1. Apparatus for detecting unlevelness in a pendulously supported fluxvalve comprising a source of alternating current signals, means to applya vertically oriented alternating magnetic field across said flux valvein response to said alternating current signals, means to receivevoltages induced in each leg of the flux valve by said alternatingmagnetic field, means to resolve said induced voltages into quadraturecomponents having a predetermined orientation with respect to said fluxvalve, means to provide output signals indicative of the magnitude andphase of each quadrature component with respect to said alternatingcurrent signals, and means for graphically displaying said outputsignals.
 2. The apparatus of claim 1 wherein the means to apply themagnetic field is a cylindrical coil adjusted to encircle a flux valveto be tested and positioned with its axis vertical.
 3. The apparatus ofclaim 2 wherein the flux valve to be tested is of the type containing aplurality of radially disposed nominally horizontal arms each containinga pickup coil, and the means to resolve said induced voltages is atransolver having individual primary windings corresponding to eachpickup coil in the flux valve to be tested, said primary windings beingspatially arranged to correspond to the pickup windings on said fluxvalve, said transolver further containing a pair of secondary windingsarranged in space quadrature and positioned so that the axis of onesecondary winding is aligned with the axis of a designated primarywinding.
 4. The apparatus of claim 3 wherein the means to provide outputsignals includes individual signal processors for each of saidquadrature components, each of said signal processors containing a phasesensitive demodulator connected to receive reference signals from saidsource of alternating current whereby each phase sensitive demodulatorproduces an output signal having a polarity representative of the phaserelationship of the corresponding quadrature component with respect tothe alternating current from said source and a magnitude indicative ofthe magnitude of the corresponding quadrature component.
 5. Theapparatus of claim 4 wherein the graphical display means is a cathoderay tube having vertical and horizontal deflection plates connected toreceive the output signals from the first and second phase sensitivedemodulators, respectively.
 6. The apparatus of claim 5 wherein eachsignal processor contains an input filter constructed to accept onlyquadrature components having a frequency substantially equal to that ofsaid alternating current signals.